This technology pertains to wireless communications networks, and in particular to wireless communications networks employing network coding.
A communication system transmits information from an information source to a destination over a communication channel. In wireless communication systems, noise and fading lead to the unreliability of the transmission. One way to overcome this unreliability is through the use of intermediate nodes or relay nodes that help the source to transmit its information to the intended destination. Communication systems using relaying operate under a fundamental principle: the information sent from one source, O1, to a destination, D, is transported independently from other information sent from another source, O2, to the same destination, D. Routers, repeaters, or relays forward the data to the destination.
Network Coding (NC) is a new area of networking in which data is manipulated inside the network to improve throughput, delay, and/or robustness. In particular, network coding allows nodes to combine several input packets into one or several output packets. At intermediate nodes, some (linear) coding may be performed on the available packets, and the resulting encoded packet can be broadcasted to different recipients simultaneously instead of transmitting each packet separately.
The area of network coding was first introduced by R. Ahlswede, N. Cai, S.-Y. R. Li, and R. W. Yeung; Network information flow; IEEE Trans. Info. Theory; July 2000, incorporated herein by reference in its entirety. Ahlswede et al present network coding as a method that allows intermediate nodes (e.g., relays) to perform some processing (coding) on the packets they receive in exchange for throughput gain.
In wireless communications, network coding is generally divided into two generic schemes: analog and digital. Analog network coding refers to coding at the signal level. The analog signals add up in the air at the node performing the network coding operation through simultaneous transmissions, i.e., by letting two signals interfere with each other intentionally. Digital network coding refers to coding at the bit level where the node performing the network coding operation will exclusive OR [XOR] (or alternatively perform other types of encoding on) the bits of the data entities to be encoded.
PCT/SE2008/050861, corresponding to WO2009041884 incorporated herein by reference, describes a novel way of performing network coding, termed as multiplicative network coding (MNC), which includes multiplying the modulated signals to perform the network coding operation. The modulated signals for transmission are assumed to be complex-valued with the information contained in the phase domain.